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Poster: Dan Keller Date: Dec 10, 2006 1:07pm
Forum: sflan Subject: whither Ralf?

Does anyone have news as to the whereabouts of Ralf?
He helped me install the sflan50 node and it needs help.

It's dead now (see below).

If Ralf doesn't resurface, is there anyone else
knowledgeable about the sflan node hardware
who could work with me sometime in the next
few months to get sflan50 back on the air?

Sflan50 (aka castro.keller.com) has 2 problems:

1. One of the antennae snapped off (have we had heavy winds
lately?) The aluminum flange that connects it to the pole
is poorly designed. Why didn't we anticipate this? When
you look at it, you see that the curved slot leaves only a
little metal actually sustaining the weight of the whole
assembly, in retrospect an obvious point of failure.
I can see that the same spots on the second antenna's
flange have stress marks and, too, will eventually snap.

2. The radios are down (despite several reboots) and are
blinking steadily. The CPU is up, though. I can see it
in my browser and can view the various node config
screens.

I lack the expertise to diagnose or cure these problems...
Advice and assistance would be much appreciated.

Thanks,
Dan Keller

Reply [edit]

Poster: Ralf Muehlen Date: Dec 11, 2006 9:16am
Forum: sflan Subject: Re: whither Ralf?

Dan,
I'm out of town till the end of the week. I can't devote a lot of time on maintenance at the moment, but I might be able to take a look at your snapped antenna.

I assume the antenna that snapped is a dish. I have always been skeptical about how those dishes shake in the wind, but never had any of the ones I installed actually fail. They are designed that way and are even supposed to hang tight with just one U-bolt. Their rated wind load is 80.5 lb at 100 mph, and 125.5 lb at 140 mph. (I assumed the manufacturer actually did wind tests.)

At any rate, the same type of dish has been up on San Bruno Mountains in very strong winds for years now without snapping off. (An older incarnation of that antenna of a slightly different design apparently did not have its screws properly tightened, and half of the reflector fell off, and yet the mounting bracket showed no sign of wear and tear.)

Without having seen the broken aluminum flange, maybe it might be possible to either have a replacement made out of steel, or to attach the flange not to the pole directly, but to a larger steel piece that in in turn has more contact points to the pole (at the possible loss of vertical adjustability).

Alternatively, there are yagi and flat panel antennas that, while being less focused, have a smaller wind profile.

I'll contact you off-channel, to come by and take a look.
Ralf